Conveyor belts comprised of transverse rods connected by links disposed along the opposite transverse edges of the belt have been in use for a long period of time. One such prior art belt uses generally U-shaped nestable links with slotted holes that allow the links to slide on the rods. The relative sliding action between the links and rods provides lateral flexibility which enables the belt to turn right or left, when such nestable links are used on both sides of the belt. When such a belt proceeds around a lateral curve, the rod ends along the inside concave edge of the belt collapse. The opposite transverse ends of the rods along the outside convex edge of the belt either remain at the same pitch as when the belt travels in a straight line direction, such as disclosed in U.S. Pat. No. 3,225,898 to Roinestad, or expand to a greater pitch in order to allow the belt to proceed around a smaller radius, as disclosed in U.S. Pat. No. 4,078,655 to Roinestad.
The collapsing or diminishing pitch of the belt along the inside edge of a lateral curve creates several problems. First of all, most ware is charged into a conveying system in a rank and file arrangement, and spacing of the ranks (crosswise rows) can only be controlled by adjusting the relative speeds of the individual feed conveyors. To make certain that the ware does not overlap, it is necessary to take into account the collapsing pitch and to also leave a safety margin in the spacing, both of which result in a drop in efficiency. If the ware being conveyed is soft in nature, the collapsing pitch can result in wrinkling of the ware. Also, if the conveyor is used in a freezing plant, the collapsing pitch can result in contact and freezing together of adjacent ware if sufficient spacing is not used.
U.S. Pat. No. 4,662,509 issued to Kaak on May 5, 1987 addresses the problem of a conveyor belt having a collapsing inner edge in a chain type conveyor belt wherein the ware support carriers are connected directly to a drive chain. The chain conveyor belt in the '509 patent uses triangular carriers consisting of a rod-shaped element and a pulling element. Along the inside edge of the conveyor belt, the rod-shaped element and the pulling element are pivotably connected to the drive chain, and the pitch of the rod-shaped elements is held constant by the connection to the drive chain. The pulling elements slant backward in the direction of travel of the belt and are pivotably connected to one of the rod-shaped elements further rearward along the belt. As the belt proceeds around a curve, the outside, free ends of the rod-shaped elements increase their spacing or pitch with respect to one another.
The conveyor belt disclosed in the '509 patent, however, has certain disadvantages or limitations. The triangular configuration of the ware carriers precludes negotiation about end pulleys or rolls, or operating through a vertical hanging take-up mechanism. The practical width of the ware carriers is limited by the triangular configuration, because the effectiveness of the pulling element diminishes with increasing width. Finally, the overlapping orientation of the pulling and rod-shaped elements gives rise to serious sanitation difficulties. The capability to clean between all elements of a belt is important when the conveyor belt is used in a food handling environment.
Parent application Ser. No. 083,272 discloses a conveyor belt designed to convey in both a straight line direction and around lateral curves. The belt is comprised of a plurality of rods and a mechanism for connecting the rods to form a length of belt. The rods extend transversely of the length of the belt between first and second transverse ends and are arranged adjacent one another along the length of the belt. The connecting mechanism includes a link mechanism disposed adjacent the first and second transverse ends of the rods for coupling adjacent pairs of rods to one another. The link mechanism also holds the first and second transverse ends of the rods at substantially the same first pitch during straight line motion of the belt, and during motion of the belt about a lateral curve, the link mechanism holds the rods to the first pitch along the transverse ends of the rods located at the inside concave edge of the lateral curve, moves the opposite transverse ends of the rods to a second greater pitch along the outside convex edge of the lateral curve as the belt proceeds from straight line to lateral curved motion, and returns the opposite transverse ends of the rods to the first pitch as the belt moves from lateral curved to straight line motion.
The conveyor belt in the parent application can be adapted to travel around lateral curves in a single direction or around lateral curves in both the right and left directions. When the belt is designed to travel around lateral curves in a single direction, the link mechanism includes both single pitch links and dual pitch links. However, when the belt is designed to travel around lateral curves in both the left and right directions, dual pitch links are disposed along both edges of the belt. The dual pitch links are pivotable between a first position and a second position. In the first position the transverse ends of the rods connected by the respective links are held at the first pitch; and, during the pivoting motion of the links from the first to the second position, are moved from the first pitch to the second pitch.
Each of the dual pitch links includes a body which has a pivot aperture and a pitch changing slot. The transverse end of one of the rods is received in the pivot aperture and the transverse ends of an adjacent one of the rods is slidably received in the pitch changing slot. A cam mechanism is provided for pivoting the dual pitch links between their first and second positions during motion around lateral curves.
A conveyor belt formed of the transverse rods and dual pitch links allows the belt to operate in a straight line direction and around curves without the problems resulting from a conveyor belt that has a collapsing inner edge as it proceeds around lateral curves.
It has been discovered that in instances where the belt will travel about lateral curves of moderate curvature in only a single direction, the advantages of using non-collapsable constant pitch links along the inner concave edge of the belt can be accomplished without the use of dual pitch links along the outside edge of the belt, by substituting properly designed slotted outside links.
It has also been discovered that the use of a link mechanism which keeps the inside rod ends at a constant pitch along the inner concave edge of a belt, both with dual pitch links as disclosed in the parent application, and with nestable U-shaped outside links as disclosed herein is particularly suitable for use in a conveying system wherein the belt travels along a helical path with the belt being arranged in a number of superimposed helically extending tiers. In such a curved tier system, less amount of belt is necessary to accommodate the same amount of an offloading surface.
Prior art helical tier systems, such as disclosed in U.S. Pat. Nos. 3,348,659 and 4,078,655 to Gerald C. Roinestad have used conveying belts with a collapsing inner edge. The successive tiers of belt in the '659 and '655 patents are supported by a support frame separate from the belt. The minimum tier height in such a system is equal to the sum of the heights of the separate belt support frame, the ware being conveyed and the belt, resulting in a system with a relatively large vertical extent. U.S. Pat. No. 3,938,651 to Alfred et al. discloses a conveying system for conveying in a helical path wherein the belt is self-supporting along both the inner and outer edges of the belt.
Another aspect of the invention is directed to the construction of the U-shaped links, particularly the construction of the portion connecting the legs of the link. It has been known in the prior art to curve the bearing surface of the connecting portion of U-shaped links. For example, the bearing surface of certain pintle chain links manufactured by the Allied-Locke Industries, Incorporated are curved. However, such prior art curved bearing surfaces for tractive links do not substantially increase the wear characteristics of the links in the manner of the present invention.